Navier-Stokes Simulations of Hypersonic Flows with Coupled Graphite Ablation

摘要

A study of graphite ablation in reentry flows is carried out by a surface ablation approach integrated with a two-dimensional axisymmetric Navier-Stokes solver. The gas-surface interaction model is based on chemical equilibrium ablation with surface mass and energy balances fully coupled with the numerical solver and can account for both surface oxidation and sublimation. The surface temperature is obtained from the steady-state ablation approximation. This numerical procedure can predict aerothermal heating, chemical species concentrations, and carbon material ablation rate over the heat-shield surface of reentry vehicles. Two-dimensional axisymmetric simulations have been performed to numerically reproduce the ablation of a graphite sphere cone that has been tested in the Interaction Heating Facility at the NASA Ames Research Center. The freestream conditions of the selected test case are typical for Earth reentry from a planetary mission. The predicted ablation rate and surface temperature assuming frozen chemistry in the flow show a good agreement with the available experimental data. The agreement is further improved freezing the nitrogen recombination reaction at the surface to be more consistent with experimental observation, which has shown nitrogen atom recombination not to occur at the graphite surface.